Give reasons for the following observations :
Why `SF_(4)` undergoes hydrolysis but not `SF_(6)`?
Or `SF_(6)` is inert towards hydroysis.
`SF_(6)` is much less reactive than `SF_(4)`.
Or (i) `SF_(4)` is easily hydrolysed whereas `SF_(6)` is not easily hydrolysed.
(ii) Sulpher exhibits greater tendency for calenation than selenium.
(iii) Sulpher has a higher tendency for catenation than oxygen.

Explanation

In `SF_(6)`, S is sterically protected by six F atoms and hence does not allow `H_(2)O` molecules to attack the S atom. Furthermore, F does not have d-orbitals to accept the electrons donated by `H_(2)O` molecules. As a result of these two resasons, `SF_(6)` does not undero hydrolysis. In constrast, in `SF_(4)`, S is not sterically protected since it is surrounded by only four F atoms. As a result, attack of `H_(2)O` molecules on S atom can take place easily and hence hydrolysis occurs.